Biomechanical Study On New Type Posterior Wall Plasticity Plates For Acetabular Posterior Wall Fractures Incorporate With Acetabular Labral Tear Injurys

Objective: With the increase of traffic and industrial accidents, acetabular fracture incidence is increasing gradually, and acetabular fractures were always caused by high-energy trauma. Acetabular posterior wall fracture is the most common kind of the acetabular fractures caused by flexion injury, 1/4 ~ 1/3 of all acetabular fractures approximately. When the hip joint under the flexion, adduction, internal rotation position,the violence from the knee was extremely easily to cause the dislocation, when the adduction angle of the legs was small, the femoral head could impact the acetabular posterior edge to cause posterior lip of acetabulum avulsion fracture or femoral neck fractures. Many internal fixation materials have been used to treat acetabular posterior wall fractures at present, and have achieved good results. But there are few reports on the acetabular labrum injury repair study,especially internal fixation treatment of the acetabular posterior wall fractures incorporate with acetabular labral tear injurys. The new type posterior wall plasticity plate designed by Professor Feng Wenling is used to solve the disadvantages of the multi block plate,for example: complex structure, the insecure connection, the inconvenient use, and can not repair the acetabular labrum,Its technical scheme is:it has a thin metal plate body,which is a long strip shaped plate, two sides of each strip plate edge extending outwards into the side hole, the side near the acetabular lip can use absorbable suture to sew up the acetabular labral tear, the other side can be screwed into the screw fixation to strengthen the anatomical plate. The curved surface shape can be matched with the ischial tuberosity. Its bend radian can be matched with acetabulum outside arc shape matched with the acetabular labrum injury. It may be become a more ideal method of the internal fixation for the treatment of the acetabular posterior wall fractures incorporate with acetabular labral tear injurys. This experiment is to provide the experimental basis of the new type posterior wall plasticity plate designed by Professor Feng Wenling for acetabular posterior wall fractures incorporate with acetabular labral tear injurys through the biomechanical comparison and research on the model.Methods: This experiment chooses 9 formalin solution soaking fresh adult pelvis specimens, including 1/3 proximal femoral shaft, with the help of the gross observation and X-ray to exclude congenital deformity, osteoporosis and bone disease. The specimens were sealed at the temperature of-20 ℃refrigerator with the double preservation bags, and taken out 24 hours before the experiment, and natural thawed at room temperature,and then sawed sacral and pubic symphysis pelvis since the median sagittal plane, and divided into about two fresh semi pelvis specimens, eliminated the soft tissue of surrounding specimens,and numbered the specimens. Then made the pelvis in the single foot standing position, then imitate the human hip flexion 90°, adduction and abduction and rotation in neutral position. According to the experimental methods of Olson, start with the line between standing top of acetabulum and acetabular center line, along the acetabular labrum, down the arc of 40°for osteotomy on the edge, to the arc of 90°for osteotomy lower margin line, took the arc of 50°of articular surface of the posterior wall longitudinally into 3 equal parts, take the foreign 1/3 as the osteotomy edge line. First, use the Kirschner wire to drill continuously according to the predetermined osteotomy line(be careful not to drill deep), and then use chisel to truncate the acetabular labrum, make the model of acetabular posterior wall 1/3 fractures incorporate with acetabular labral tear injurys, and then divided into three groups randomly, The fractures were fixed with new type posterior wall plasticity plate in A and B group, and use absorbable suture to sew up the acetabular labral tear in A group, and with common fracture plate in C group. Then conduct the biomechanical experiment, including axial compression test and load test of dislocation. The longitudinal displacements, loading of failed internal fixation and axial stiffness,and the loadings when the femoral heads dislocated of hip joint adduction 20° were measured by axial loading experiments and compared between groups.Results: In the axial compression test,under the same loading, longitudinal displacements of B group were shorter than that of C group, longitudinal displacements of A group were shorter than that of B group(P<0.05). There is significant difference, shows the stability of A group >B group >C group. On this basis, each loading of failed internal fixation respectively in A group(991.72 + 4.47) N, B group(884.90 + 3.35) N, C group(729.67 + 2.91) N. A group >B group >C group, there is significant difference(P < 0.05). The fixed axial stiffness in each group were group A(330.57 + 1.49) N/mm, B group(294.96 + 1.11) N/mm, C group(243.22 + 0.97) N/mm. A group >B group >C group, there is significant difference(P < 0.05). Because when the loading of failed internal fixation is larger, the axial stiffness is bigger, the ability of internal fixation of resistance to deformation is stronger,the hip is more stable, so further illustrates the stability of A group >B group >C group. At the same time to test and verify the maximum load of each group, we design the specimen when the femoral heads dislocated of hip joint adduction 20° on the basis of the original, conduct the load test of dislocation, the loadings when the femoral heads dislocated of each group were: A group(1171.50 + 23.26) N, B group(1067 + 19.65) N, C group(980.17 + 13.01) N. A group >B group >C group, there is significant difference(P < 0.05).Conclusions: This experiment is to establish the model of acetabular posterior wall fractures incorporate with acetabular labral tear injurys, and be fixed with common fracture plate and new type posterior wall plasticity plate which use absorbable suture to sew up the acetabular labral tear respectively,to compare and analyse the stability of the acetabular posterior wall fractures incorporate with acetabular labral tear injurys were fixed with new type posterior wall plasticity plate, and use absorbable suture to sew up the acetabular labral tear, and with common fracture plate through the method of the biomechanics,to make clear the advantage of new type posterior wall plasticity plates and the significance of repairing the acetabular labrum for the stability of the acetabular posterior wall fracture. This experiment draws the conclusion at last: new type posterior wall plasticity plate can be used for internal fixation management of the posterior wall acetabular fractures incorporate with acetabular labral tear injurys, and the effect is favorable.